The present invention relates generally to connectors for optical fibers, and particularly to a connector that secures an outer insulating jacket located on an inner optical fiber in the connector to insure protection of the inner fiber during handling and use of the connector.
Optical fiber cables generally comprise a center optical fiber, the diameter of which may be on the order of 125 microns which size includes a thin cladding of material having an index of refraction different from that of an inner, light conducting core of the fiber. The optical fiber is also coated with one or more thermoplastic materials to a diameter of typically 900 microns. Such a fiber is surrounded by an aramid yarn, which serves as a strain relief member to protect the optical fiber (generally rather fragile) from breaking. Over the aramid yarn is disposed an insulating jacket, of PVC material, for example, the jacket being necessary to portect the optical fiber against damage from sources outside of the cable, as well as to protect the fiber by increasing the radii of any bends occurring during installation, removal or any other type of handling or use of the cable.
In providing the ends of fiber optic cables with means for connecting to another fiber optical cable or for connecting to light sensing devices, it is important that the ends of both the aramid yarn and the outer jacket be secured within the body of the connecting means. Certain jacket materials shrink due to changes in temperature, such that if left unattached, the jacket separates from the connector body and thereby exposes the yarn and fiber. Plenum grade materials, i.e., jacket materials that may be subject to smoke and fire in the "plenum space" above suspended ceilings, are particularly subject to shrinkage at room temperature.
It is known to secure the aramid fibers in a connector structure to maintain the necessary strain relief protection for the optical fiber. Patent art showing such retention includes U.S. Pat. No. 4,863,325 to Anderson et al., U.S. Pat. No. 4,790,622 to Levinson et al., U.S. Pat. No. 4,812,009 to Carlisle et al., and U.S. Pat. No. 4,804,252 to Beltzer et al. In the Carlisle et al. reference, FIG. 3 shows a yarn 33 secured between an outer, crimped sleeve 65 and an extension 55 of a barrel member 43. In Beltzer et al., a yarn 30 of optical fiber cable 26 is folded back over sleeve 42 and a second sleeve 46 disposed over the folded yarn. Sleeve 42 has a knurled surface 44. Sleeve 46 is crimped over the yarn and knurled surface of sleeve 42.
What has been essentially neglected in the art has been the need to secure the outer insulating jacket in the connector body so that the inner optical fiber is and remains protected during use. The securing of the jacket, however, must not compress and restrain the optical fiber in the jacket, and should allow the coated fiber to move freely within the jacket, within the yarn and within the connector body. In the case of the above Carlisle et al. patent, for example, outer sleeve 65 is crimped on the end of the jacket in a manner that tends to compress and restrain inner fiber 26 so that the fiber is not free to move longitudinally within the jacket and connector body.
In the above Beltzer et al. patent, the yarn is crimped between the knurled surface 44 of inner sleeve 42 and outer sleeve 46. An end of outer jacket 32 of cable 26 is located within the inner ferrule, but is not secured therein by crimping, as the inner ferrule is a non-compressible member.